Recovering hydrocarbons from subterranean zones relies on drilling wellbores.
Wellbores are made using surface-located drilling equipment which drives a drill string that eventually extends from the surface equipment to the formation or subterranean zone of interest. The drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string includes a drill bit for drilling (or extending) the wellbore. Drilling fluid usually in the form of a drilling “mud” is typically pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface. Drilling fluid may also be used to help control bottom hole pressure to inhibit hydrocarbon influx from the formation into the wellbore and potential blow out at surface.
Bottom hole assembly (BHA) is the name given to the equipment at the terminal end of a drill string. In addition to a drill bit a BHA may comprise elements such as: apparatus for steering the direction of the drilling (e.g. a steerable downhole mud motor or rotary steerable system); probes for measuring properties of the surrounding geological formations (e.g. probes for use in well logging); probes for measuring downhole conditions as drilling progresses; systems for telemetry of data to the surface; stabilizers; drill collars, pulsers and the like. The BHA is typically advanced into the wellbore by a string of metallic tubulars (drill pipe).
A downhole probe may comprise any active mechanical, electronic, and/or electromechanical system that operates downhole. A probe may provide any of a wide range of functions including, without limitation, data acquisition, measuring properties of the surrounding geological formations (e.g. well logging), measuring downhole conditions as drilling progresses, controlling downhole equipment, monitoring status of downhole equipment, measuring properties of downhole fluids and the like. A probe may comprise one or more systems for: telemetry of data to the surface; collecting data by way of sensors (e.g. sensors for use in well logging) that may include one or more of vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, and others; acquiring images; measuring fluid flow; determining directions; emitting signals, particles or fields for detection by other devices; interfacing to other downhole equipment; sampling downhole fluids, etc. Some downhole probes are highly specialized and expensive.
Downhole conditions can be harsh. Exposure to these harsh conditions, which can include high temperatures, vibrations, turbulence and pulsations in the flow of drilling fluid past the probe, shocks, and immersion in various drilling fluids at high pressures can shorten the lifespan of downhole probes and increase the probability that a downhole probe will fail in use. Supporting and protecting downhole probes is important as a downhole probe may be subjected to high pressures (20,000 p.s.i. or more in some cases), along with severe shocks and vibrations. Replacing a downhole probe that fails while drilling can involve very great expense.
An example application of downhole probes is steering the direction of drilling in directional drilling. In some directional drilling applications the inclination and compass heading of the hole is continuously measured by systems in a downhole probe. Course corrections may be made based on information provided by the downhole probe. An example directional drilling system includes a mud motor drilling system in which a mud motor is powered by the flow of drilling fluid to operate the drill. In such systems the drill may be steered using a “bent sub” located near the drill bit. The bent sub causes the drill to address formations at an angle to the longitudinal axis of the drill string. The drill string can be turned to change the angle at which the drill engages the formation being drilled into. The drill may be steered by turning the drill string as drilling progresses to cause the wellbore to follow a desired trajectory.
A downhole probe may include instrumentation that determines the orientation of the downhole probe. Information from such instrumentation in the downhole probe may be used to make decisions regarding how to steer the drill. In such systems the offset angle of the bent sub relative to the downhole probe may be measured and taken into account in interpreting information from the downhole probe.
A downhole probe may communicate a wide range of information to the surface by telemetry. Telemetry information can be invaluable for efficient drilling operations. For example, telemetry information may be used by a drill rig crew to make decisions about controlling and steering the drill bit to optimize the drilling speed and trajectory based on numerous factors, including legal boundaries, locations of existing wells, formation properties, hydrocarbon size and location, etc. A crew may make intentional deviations from the planned path as necessary based on information gathered from downhole sensors and transmitted to the surface by telemetry during the drilling process. The ability to obtain and transmit reliable data from downhole locations allows for relatively more economical and more efficient drilling operations.
Various techniques have been used to transmit information from a location in a bore hole to the surface. These include transmitting information by generating vibrations in fluid in the bore hole (e.g. acoustic telemetry or mud pulse telemetry) and transmitting information by way of electromagnetic signals that propagate at least in part through the earth (EM telemetry). Other telemetry systems use hardwired drill pipe, fibre optic cable, or drill collar acoustic telemetry to carry data to the surface.
Sensors for use in directional drilling are typically located in a downhole probe or instrumentation assembly suspended in a bore of a drill string near the drill bit. The probe is typically suspended within the bore of a drill collar. As it is secured uphole, the probe is subject to the fluid initiated harmonics and torsional acceleration events from stick slip which can lead to side-to-side and/or torsional movement of the probe. This can result in damage to the electronics and sensors in the probe or sections of the housing of the probe can come unthreaded from each other.
The following references describe various centralizers that may be useful for supporting a downhole electronics probe centrally in a bore within a drill string. The following is a list of some such references: US2007/0235224; US2005/0217898; U.S. Pat. Nos. 6,429,653; 3,323,327; 4,571,215; 4,684,946; 4,938,299; 5,236,048; 5,247,990; 5,474,132; 5,520,246; 6,429,653; 6,446,736; 6,750,783; 7,151,466; 7,243,028; US2009/0023502; WO2006/083764; WO2008/116077; WO2012/045698; and WO2012/082748.
There remains a need for ways to support downhole probes in a way that provides improved protection against mechanical shocks and vibrations and other downhole conditions.